<html>
<body>
<script src="https://cdn.jsdelivr.net/npm/vue"></script>
<div id="app-3">
    <p v-if="seen">现在你看到我了</p>
</div>
<script>
var app3 = new Vue({
  el: '#app-3',
  data: {
    seen: true
  }
})
</script>
</body>
</html>